San is indeed the Japanese word for three. It can mean other things too
(it
depends on the kanji used to write it; Japanese is riddled with
homophones), but in this context it is most likely three:
———–—
———
–————

The Chariot may 'run down' one Soldier, allowing it to capture up to two
pieces. Sorry for any confusion.
The Chariot's ability to 'run down' an opposing Soldier is similar to
the XiangQi Cannon shot using a screen. Except that this particular
screen is captured, and it is not necessary that another piece be
captured following this.

I haven't played it yet, but the game looks good to me also. There's one thing I think should be added to the rules to clarify the Chariot's power of 'running down' soldiers: it wasn't clear to me whether they could run down any number of soldiers in a line, or only one. From the ZRF it seems to be only one.

It is quite easy to construct a real-world board using cardboard, scissors,
straight-edge and a felt-tip pen. The disc can be made from the same
material.
And the visualization of the Cavalry leap is simply an orthogonal
translation to the second cell(a cell which is oriented in a similar
manner). For example:
/\ /\
/__\/__\
If a friendly piece is at the first, another such translation can be made
in any direction. It is not meant to be equivalent to the FIDE leap.
Since this is a triangle field, that particular form of leap is not
possible. Its similarity to the Ko Shogi Cavalry leap in its ability to
use a friendly piece to continue its particular leap.

The triangular cells on this chessboard make it very difficult to work out
lines of strategy by yourself, let alone play an OTB game. This means
you
have to construct the pieces and the board yourself, which in my opinion
is more trouble than the game might be worth.
And by the way, not everyone understands Shogi. I also found the
Cavalry's movement, though meant to be the equivalent of the Knight in
FIDE chess, was particularly difficult to visualize.